Portable ventilator system

ABSTRACT

A portable ventilator uses a Roots-type blower as a compressor to reduce both the size and power consumption of the ventilator. Various functional aspects of the ventilator are delegated to multiple subassemblies having dedicated controllers and software that interact with a ventilator processor to provide user interface functions, exhalation control and flow control servos, and monitoring of patient status. The ventilator overcomes noise problems through the use of noise reducing pressure compensating orifices on the Roots blower housing and multiple baffling chambers. The ventilator is configured with a highly portable form factor, and may be used as a stand-alone device or as a docked device having a docking cradle with enhanced interface and monitoring capabilities.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a divisional of U.S. patent application Ser.No. 10/912,747 entitled PORTABLE VENTILATOR SYSTEM filed Aug. 4, 2004,now issued as U.S. Pat. No. 7,188,621, and which claims the benefit ofpriority from U.S. Provisional Patent Application Ser. No. 60/492,421,filed Aug. 4, 2003, the entirety of the disclosures of which areexpressly incorporated herein by reference.

FIELD OF THE INVENTION

This invention relates to the field of medical ventilators, and morespecifically to a self-contained portable ventilator.

A portion of the disclosure of this patent document contains materialwhich is subject to copyright protection. The copyright owner has noobjection to the facsimile reproduction by anyone of the patent documentor the patent disclosure, as it appears in the Patent and TrademarkOffice file or records, but otherwise reserves all copyrights associatedwith this document.

BACKGROUND

Ventilators for patients requiring breathing assistance havetraditionally been large, heavy, power-hungry devices that have providedlittle if any mobility to a patient. Recent advances in compressortechnology, such as those described in U.S. Pat. No. 6,152,135 issued toDeVries et al., have allowed a reduction in size and power requirementsof ventilators, for the first time allowing the manufacture ofventilators that were able to provide a limited degree of self-containedportability. Outfitted with battery packs, these portable ventilatorscould be attached to a wheel chair, providing a patient the ability tomove about for a limited amount of time without having the ventilatorconnected to a power supply main.

Ventilators of the prior art have become smaller and more transportablewhile maintaining the ability to deliver complex breath modes bytypically using low pressure rotary drag compressors as the breathdelivery mechanism. The drag compressors may either be variable speed orconstant speed. Variable speed ventilator compressors operate by rapidlyaccelerating from a standstill to provide inhalation assistance(inspiration) to a patient, then decelerate rapidly to allow a patientto exhale. The rapid acceleration and deceleration of prior art variablespeed compressor ventilators require the compressor's drive circuitry tohandle very high currents, necessitating bulky and expensive powersystems and considerable standby battery power when the ventilator isnot connected to a power main.

Constant speed compressors do not need the bulky power systems ofvariable-speed compressors, but have inherent inefficiencies because thecompressor continues to run and consume power even at times when no airis being supplied to the patient (such as during exhalation). The powerconsumption can be reduced by recirculating the compressor's output airflow to the compressor's intake during exhalation. However, even thereduced power consumed significantly reduces the amount of time theventilator can be operated from on-board battery power.

SUMMARY OF THE INVENTION

The present invention comprises a portable ventilator that uses a small,low-inertia, high-speed, high-efficiency Roots-type blower invariable-speed mode. Roots-type blowers are known for high-efficiencyand small size. However, they are inherently noisy, and have in the pastnot been suited for use in medical ventilators, where excessive noise isdisruptive to patients, who often require around-the-clock breathingassistance. The ventilator of the present invention overcomes the noiseproblems of prior art Roots-type blowers through the combined use ofnovel noise reducing pressure compensating orifices on the Roots blowerhousing and multiple baffling chambers within the ventilator's housing.The use of a Roots-type compressor in a variable-speed mode, togetherwith specially configured flow control and power systems, reduces boththe size and power consumption of the ventilator as a whole. Embodimentsof the invention provide full ventilator functionality, including thecapability of operating in both volume and pressure control modes, insmall, truly portable units that for the first time provide realmobility to patients. In one embodiment, the ventilator is a portable,self-contained ventilator that approximates the size of a small laptopcomputer while providing several hours of battery powered, full-servicebreathing assistance.

In one or more embodiments of the invention, the ventilator employs aheavier Roots blower with greater inertia in constant speed mode. Theextra ordinary efficiency of the Roots blower permits size and weightreductions to a degree previously unattainable in a full featuredventilator capable of delivering complex breath modes.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of the front face of a portable ventilatorin accordance with one or more embodiments of the invention.

FIG. 2A is perspective view of the front of a ventilator systemincluding a portable ventilator, a docking cradle and a ventilatormonitor, in accordance with one or more embodiments of the invention.

FIG. 2B is a perspective view of the rear of the ventilator system ofFIG. 2A.

FIG. 3 is a block diagram of a functional architecture for a portableventilator system in accordance with one or more embodiments of theinvention.

FIG. 4 is a block diagram of an electronic architecture for a portableventilator system in accordance with one or more embodiments of theinvention.

FIG. 5 is a block diagram of an electronic architecture for a dockingcradle in accordance with one or more embodiments of the invention.

FIGS. 6A and 6B are block diagrams illustrating the general context of asoftware architecture for a portable ventilator system in accordancewith one or more embodiments of the invention.

FIG. 7 is a pneumatic diagram of a portable ventilator in accordancewith one or more embodiments of the invention.

FIG. 8 is a top level block diagram of an exhalation servo controlsystem in accordance with one or more embodiments of the invention.

FIG. 9A is a block diagram of a mechanical assembly portion of anexhalation servo control system in accordance with one or moreembodiments of the invention.

FIG. 9B is a block diagram of an electronic assembly portion of anexhalation servo control system in accordance with one or moreembodiments of the invention.

FIG. 9C is a block diagram of a software control portion of anexhalation servo control system in accordance with one or moreembodiments of the invention.

FIG. 10 is a block diagram of a blower assembly in accordance with oneor more embodiments of the invention.

FIG. 11 is an exploded view of a blower assembly in accordance with oneor more embodiments of the invention.

FIG. 12 is a perspective view of a pair of Roots blower impellers inaccordance with one or more embodiments of the invention.

FIGS. 13A and 13B are views of a ventilator apparatus having silencerchambers with perforated tubes, in accordance with one or moreembodiments of the invention.

FIGS. 14A-14D are various views of a Roots blower housing, illustratinggraduated slots at the air outlets, in accordance with one or moreembodiments of the invention.

DETAILED DESCRIPTION

A portable ventilator system is described. In the following description,numerous specific details, such as physical dimensions for one or moreembodiments, are set forth to provide a more thorough description of theinvention. It will be apparent, however, to one skilled in the art, thatthe invention may be practiced without these specific details. In otherinstances, well known features have not been described in detail so asnot to obscure the invention.

Embodiments of the invention implement a portable ventilator that uses aRoots-type blower operating in a variable speed mode as the breathdelivery mechanism. The efficiencies and reduced size requirementsresulting from the use of a Roots-type blower, together with novel soundmuffling techniques and electronic control systems, allow the ventilatorto be reduced in size to be comparable to a palmtop computer. Weight andpower consumption may likewise be reduced. The ventilator of the presentinvention provides true, extended mobility to patients who requirecontinuous breathing assistance, facilitating a significant improvementin their quality of life.

I. Embodiment of Ventilator System with Portable Ventilator, DockingCradle and Monitor

In one or more embodiments of the invention, a portable ventilatorsystem includes a portable ventilator, a docking cradle and a monitor.The portable ventilator is preferably, though not necessarily, a small,lightweight, self-contained life support device that is highly portable.In stationary applications, the portable ventilator may be placed into adocking cradle that acts as a simple structural support, possiblyincluding a power supply and/or recharging system, or that expands theportable ventilators interface capabilities. For example, the dockingcradle may also include a graphics monitor for enhanced displaycapabilities.

A. Portable Ventilator Enclosure

In one or more embodiments, the portable ventilator may be packagedwithin a molded enclosure. In some embodiments, the enclosure isco-molded with a soft rubber boot. Preferrably, though not necessarily,the enclosure is configured to have a relatively compact form factor.For example, in one embodiment, an enclosure that is 10″×6″×2″ maycontain the apparatus needed for a patient to receive proper ventilatorsupport from a highly portable unit. Other embodiments may useenclosures with varying form factors.

FIG. 1 is a diagram illustrating a perspective view of the front face ofa portable ventilator, in accordance with one or more embodiments of theinvention. In the illustrated embodiment, the pneumatic connections 101may be made on the left and right sides, e.g., below the centerline ofventilator enclosure 100. Electrical interconnects 102 may be made onthe lower edge of the backside of enclosure 100 (e.g., to provide acradle interface). The electrical interconnects may also be made on theleft and/or right sides of enclosure 100, e.g., above the centerline.

The ventilator enclosure may include a user interface 106. For example,user interface 106 may be implemented relatively inexpensively in oneembodiment with LEDs and a membrane switch panel. Another embodiment mayimplement a graphical user interface 106 using a color LCD and touchscreen.

In one or more embodiments, the top of ventilator enclosure 100 mayinclude a collapsible handle 103 that acts as a table stand when foldedand collapses flush against the enclosure. Hand/shoulder strapconnection points 104 may be built into enclosure 100. One or moreembodiments may also implement a low-profile, dovetail-style mountingmechanism on the rear of enclosure 100 to facilitate pole, wall orbed-rail mounting without interfering with non-mounted desktopapplications.

In one or more embodiments, battery port 105 may be provided onenclosure 100 to accommodate an internal, removable battery pack.Battery port 105 is preferably equipped with a latch and eject mechanismto insure a reliable connection when in use, and easy swapping of theremovable battery pack, even when the enclosure is seated in a cradle(described below).

Enclosure 100 may be designed to drop into a docking cradle for raisedsupport and/or to establish a connection between the portable ventilatorand cradle electronics. An embodiment of a docking cradle is describedbelow.

B. Docking Cradle and Monitor

FIGS. 2A and 2B provide a perspective views of the front and rear of aportable ventilator system, comprising a portable ventilator, a dockingcradle and a monitor, in accordance with one or more embodiments of theinvention. As shown, docking cradle 200 may include a base 201A and acradle arm 201B. A monitor 202 may be attached to arm 201B to provide adisplay for expanded ventilator monitoring capabilities. Portableventilator enclosure 100 is shown docked into base 201A of cradle 200.

In one or more embodiments, base 201A is designed to function as asimple table stand, without any internal power or logic components.However, in most embodiments, internal electronics are included toprovide an intelligent docking station capable of supplying power andexpanding the interface capabilities of the portable ventilator. In thelatter case, base 201A provides an electrical interconnection with thedocked ventilator, e.g., through the lower, back edge of the ventilator.Arm 201B may be removably attached to base 201A to provide a support forthe optional monitor 202. Power and data cables between electronics inthe cradle base 201A and monitor 202 may be hidden within the structureof arm 201B.

Cradle 200 may include a mechanical interlock to ensure that the dockedventilator cannot fall out. As with the ventilator enclosure 100, cradle200 may also incorporate a dovetail-style mounting mechanism tofacilitate wall or bed-rail mounting. The docking cradle 200 and monitor202 may each contain injection molded components.

C. Ventilator System Functional Architecture

FIG. 3 is a block diagram of a ventilator system functionalarchitecture, in accordance with one or more embodiments of theinvention. The ventilator pneumatics may be based on a Roots blower 300that draws room air through inlet filter 310 and delivers pressurizedgas through inspiratory port 311 to the patient. The pneumatic systemmay support both single limb and dual limb patient circuits, allowingexhalation valve 301 to be implemented either externally or internallywith respect to ventilator enclosure 100. Exhalation control port 302and PEEP (positive end-expiratory pressure) control 303 generate a pilotpressure that closes exhalation valve 301 during inspiration and opensit against a software controlled PEEP pilot pressure during exhalation.Scavenging port 316 may be used to recycle or recirculate the compressedair that is not used by the patient during exhalation.

The ventilator 100 may deliver blended gas using an optional internal O₂blender 304. The blended gas delivery in inspiratory limb 312 may bemonitored via an external FIO₂ (fraction of inspired oxygen) sensor 305coupled to FIO₂ interface 313, and displayed on user interface 306.Similarly, the patient's blood O₂ level may also be monitored via anexternal pulse oxygen sensor 314 coupled to optional internal pulseoximeter 307, and displayed on user interface 306. When high-pressureoxygen is supplied to O₂ inlet port 308, the ventilator 100 may drive anexternal nebulizer 309 via nebulizer drive port 350 for the delivery ofaerosolized drugs to the patient while, at the same time, compensatingfor the added gas delivery.

One or more embodiments may use a wye (“Y”) junction 325 to coupleinspiratory limb 312 and expiratory limb 326 to the main ventilator tubeto the patient. Airway and flow sensor lines 327 from wye junction 325enter ventilator enclosure 100 via sense ports 328. Transducer (XDCR)manifold 329 converts the airway and flow values from sense ports 328into electrical sense signals for use in the ventilator control loop.

In one or more embodiments, the portable ventilator (100) may operatefrom externally supplied DC power received through external powerconnector 317 (e.g., from external battery charger 318A, externalbattery 318B, AC/DC adapter 318C, DC bus 318D, etc.). A cradle interface319 may allow external power to be supplied to the ventilator withoutusing a cable plug-in. For example, the ventilator enclosure 100 may bedropped into docking cradle 200, where contacts in both devicesautomatically engage to provide a power path and/or data path. Also,removable battery 321 may be seated in removable battery bay 320 for useof the ventilator as a portable, stand-alone device. The ventilator maybe configured with an internal bridge battery (322) to providecontinuous power to the ventilator during a swap of removable batteries(321). Battery charger 323 may be used to charge removable battery 321and/or bridge battery 322 when an external power source is connected tothe ventilator enclosure 100. An external removable battery charger(324) may be used to charge extra batteries.

In the embodiment shown in FIG. 3, docking cradle 200 includes aventilator interface 330 that mates with cradle interface block 319 ofventilator 100 to transfer power and provide electrical connections withinterface electronics internal to cradle 200. Optional internal AC/DCadapter 331 within cradle 200 may provide a source of DC power toventilator 100 via interface blocks 319 and 330, as well as to thecircuitry within cradle 200 and monitor 202. Cradle 200 may additionallyor alternatively have a DC connector that receives DC power from anexternal source (e.g., sources 318A-318D).

Cradle 200 may be used to expand the ventilator's interface capabilitiesto include, for example: a remote alarm/nurse call interface 332 with anoutput alarm cable; a remote access modem 333; an ISP/debug port 334(service and maintenance port); an ETCO₂ (end tidal carbon dioxide)monitor 336 coupled to an external ETCO₂ sensor 335; a patient monitorinterface 337 supporting patient monitor system s (such as HP Valuelinkand SpaceLabs Flexport); a removable memory card slot 338 for supportingremovable memory card 339; and a monitor interface/controller 340. Theremovable memory card 339 may be used to ease movement of informationbetween the ventilator and a personal computer for data review andprinting.

Monitor 202, coupled to arm 201B of cradle 200 is an optional displayunit capable of, for example, depicting waveforms, loops, and trend datacontinuously.

D. Ventilator Electronic Architecture

In one or more embodiments, the portable ventilator electronicarchitecture may be divided into three major subsystems: a ventilatorcore subsystem, a user interface subsystem, and a power subsystem. Eachsubsystem may include one or more software programmable microcontrollersdistributed through the subassemblies along with a variety of digital,analog and power circuitry. Other embodiments may divide the electronicarchitecture along different lines, or not divide the architecture atall.

FIG. 4 illustrates one embodiment of the ventilator electronicarchitecture having a ventilator core (VC subsystem) 401, a userinterface (UI subsystem 400 and a power subsystem 402. Each subsystem isdescribed in more detail below.

1. Ventilator Core Subsystem

In the embodiment of FIG. 4, VC subsystem 401 includes electronics forimplementing the core gas delivery functions of the portable ventilator.A software program running on the ventilator processor 443 may controlthe overall ventilator core functionality by commanding and monitoringmicrocontrollers located within each functional subassembly or module.Each of these microcontrollers may run software programs dedicated to aspecific task or tasks of the respective subassembly. In otherembodiments, a single processor may be used to execute the tasks ofmultiple subassemblies. In the illustrated embodiment, VC subsystem 401includes ventilator processor 443 in communication with respectiveprocessors within Roots blower module 444, exhalation control module454, blender module 461, and transducer module 470. (In an alternateembodiment, two or more of modules 444, 454, 461 and 470 may be servedby a single module processor.)

In Roots blower module 444, blower processor 445 may control the blowerspeed through software commutation of a brushless DC motor (BLDC 453)attached to the impellers of a Roots blower. Inverter 449 may be used toconvert the logic level commutation signals from blower processor 445into high-power AC current to drive BLDC motor 453. Multiple magneticsensors (e.g., analog Hall sensors 452) within BLDC motor 453 transmitsense signals to blower processor 445 to determine rotor position andspeed. An ADC (analog-to-digital converter) circuit may be providedinternal to or external to the blower processor IC for the purpose ofsampling and converting sense signals, such as those from Hall sensors452, into digital values for blower processor 445.

Microphones 451 at the Roots blower intake and outlet ports may be usedto monitor the audible noise of the Roots blower apparatus. Themicrophone signals are also sampled by the ADC circuit before beingprocessed within blower processor 445. Amplifier circuits 447 and 448may be used to amplify and filter the microphone and motor sensesignals, respectively, prior to the ADC circuit. To reduce the systemnoise level, blower processor 445 may generate “anti-noise” signals tocancel the blower noise. The anti-noise channels (e.g., one each for thenoise at the intake and outlet ports of the blower) may be amplified viapower amplifiers 446 that in turn drive a pair of speakers 450 locatedwithin the blower ductwork.

The blower processor 445 may include (either on-chip or off-chip) dataSRAM, program FLASH memory, and calibration EEPROM. The FLASH and EEPROMmemory may be in-system programmable to facilitate manufacturing,service and field software updates. Blower processor 445 may communicatewith ventilator control processor 443 via a high-speed synchronousserial port (SSIO 479).

Blower processor 445 may provide a mechanism for calibrating theelectronics of blower module 444, and for storing the calibration datawithin its EEPROM. Blower processor 445 may provide the additionalability to monitor the health of the electronics of blower module 444and generate self-test feedback to ventilator processor 443 (or aseparate test apparatus).

Within exhalation control module 454, exhalation processor 455 maycontrol multiple solenoid valves that generate and pass pilot pressureto the exhalation valve balloon diaphragm. Solenoid valve drivers 456translate the logic level control signals generated by exhalationprocessor 455 into high-power DC current to actuate exhalation controlvalve 459 and PEEP pilot valves 460. Exhalation processor 455 monitorsPEEP pressure transducer 458 to enable closed loop control of PEEP pilotvalves 460. The analog signals from transducer 458 maybe amplified andfiltered by amplifier 457 prior to being A/D converted and sampled bythe ADC circuit for exhalation processor 455.

As with blower processor 445, exhalation processor 455 may include(either on-chip or off-chip) data SRAM, program FLASH memory, andcalibration EEPROM. The FLASH and EEPROM memory may be in-systemprogrammable to facilitate manufacturing, service and field softwareupdates. Exhalation processor 455 may communicate with ventilatorcontrol processor 443 via a high-speed synchronous serial port (SSIO480).

Exhalation processor 455 may provide a mechanism for calibrating theelectronics of exhalation control module 454, and for storing thecalibration data within its EEPROM. Exhalation processor 455 may providethe additional ability to monitor the health of the electronics ofexhalation control module 454 and generate self-test feedback toventilator processor 443 (or a separate test apparatus).

Within blender module 461, blender processor 462 controls the flow ofoxygen in the system, controls the optional nebulizer drive function,and monitors the external FIO₂ sensor via FIO2 sensor interface 469.Solenoid valve drivers 463 translate the logic level control signalsgenerated by blender processor 462 into high-power DC current to actuateblender valves 468 and nebulizer valve 467. Blender processor 462monitors oxygen pressure transducer 465 to enable closed loop control ofblender valves 468. The analog signals from transducer 465 and interface469 maybe amplified and filtered by amplifier 464 and 466, respectively,prior to being A/D converted and sampled by the ADC circuit for blenderprocessor 462.

As with the blower and exhalation processors, blender processor 462 mayinclude (either on-chip or off-chip) data SRAM, program FLASH memory,and calibration EEPROM. The FLASH and EEPROM memory may be in-systemprogrammable to facilitate manufacturing, service and field softwareupdates. Blender processor 462 may communicate with ventilator controlprocessor 443 via a high-speed synchronous serial port (SSIO 481).

Blender processor 462 may provide a mechanism for calibrating theelectronics of blender module 461, and for storing the calibration datawithin its EEPROM. Blender processor 462 may provide the additionalability to monitor the health of the electronics of blender module 461and generate self-test feedback to ventilator processor 443 (or aseparate test apparatus).

Within transducer module 470, pressure processor 471 measures criticalsystem pressures and manages periodic auto zero and sense line purgefunctions. Solenoid valve drivers 472 translate the logic level controlsignals generated by pressure processor 471 into high-power DC currentto actuate autozero valves 473 and purge valves 474. Pressure processor471 monitors flow sensor pressure transducer 477 and airway and blowerpressure transducers 478.

Amplifiers 476 amplify and filter the sense signal outputs oftransducers 477 and 478 before those sense signals are sampled andprocessed by pressure processor 471. In one embodiment, two parallelamplifiers may be dedicated to flow sensor pressure transducer 477. Oneamplifier may provide a high-gain, narrow-range, offset-compensated flowtrigger channel. The offset compensation is provided using asoftware-controlled DAC (digital-to-analog converter) circuit 475. Asecond channel may provide a lower gain amplifier to cover the fullbi-directional dynamic range of flow into and out of the patient.Amplifiers 476 also provide amplified airway gauge pressure and blowerdifferential pressure signals.

As with the other module processors, pressure processor 471 may include(either on-chip or off-chip) data SRAM, program FLASH memory, andcalibration EEPROM. The FLASH and EEPROM memory may be in-systemprogrammable to facilitate manufacturing, service and field softwareupdates. Pressure processor 471 may communicate with ventilator controlprocessor 443 via a high-speed synchronous serial port (SSIO 482).

Pressure processor 471 may provide a mechanism for calibrating theelectronics of transducer module 470, and for storing the calibrationdata within its EEPROM. Pressure processor 471 may provide theadditional ability to monitor the health of the electronics oftransducer module 470 and generate self-test feedback to ventilatorprocessor 443 (or a separate test apparatus).

2. User Interface Subsystem

User interface (UI) subsystem 400 includes the electronics to create theinterface to the device user and external peripherals. In one or moreembodiments, UI subsystem 400 may provide the user with information,such as audible and visual feedback regarding the patient status,machine status, alarm conditions, and control settings. UI subsystem 400monitors the user inputs (e.g., knob and buttons) and communicatessettings to ventilator processor 443 of ventilator core subsystem 401via a serial channel (e.g., UART 438). Also, in one or more embodiments,UI subsystem 400 monitors and controls power subsystem 402, maintainsdevice configuration and control settings in non-volatile memory, actsas a recorder of events and user actions, and communicates with anyaccessory devices (e.g., docking cradle 200, internal pulse oximeter307, etc.).

Within UI subsystem 400, user interface processor 403 executes asoftware program that controls the overall user interface functionality.The program FLASH memory associated with user interface processor 403may be in-system programmable to facilitate manufacturing, service andfield software updates. In one or more embodiments, certain tasks, suchas refreshing displays and scanning keys, may be delegated to aprogrammable microcontroller and/or dedicated hardware controllerslocated within user interface subassemblies. The functionality ofpossible UI subassemblies is described below.

The ventilator user interface may be implemented with a variety ofdisplay and input/output mechanisms. For example, one user interfaceembodiment (labeled as high end user interface 404) utilizes a color LCD(liquid crystal display: e.g., TFT or VGA) graphics panel 429 and ananalog touch screen overlay 431 to provide a flexible user interfacewith high information content. Interface 404 is coupled to UI processor403 via bus 435. LCD controller 432 may perform the time-intensive taskof refreshing LCD 429 from a RAM image buffer (on-chip or off-chip) viaa high-speed LVDS (low voltage differential signaling) interface 428.The UI software may restrict updates of the image buffer to time periodsduring which the display content actually changes.

Backlight inverter 430 powers the LCD backlight. Screen brightness maybe controlled by the UI software using backlight DAC 433. The touchscreen. ADC/controller 434 performs scans of the touch screen overlay431, and provides the UI software with an interrupt and data duringperiods of touch activity.

Another user interface embodiment alternatively or additionally may usea low end user interface 408 including, for example, a combination ofdot matrix, seven-segment and/or discrete LEDs (represented as LEDmatrix 414) and a membrane key matrix 415. LED matrix 414 is driven byLED source drivers 416 and LED sink drivers 417. IO (input/output)processor 410 may perform the task of refreshing the LED matrix 414 froma RAM image buffer. The UI software may update the image buffer when itscontent changes. IO processor 410 also performs the task of scanning keymatrix 415 and providing the UI software with an interrupt and dataduring periods of key activity.

Both user interface options (high-end interface 404 and low endinterface 408) may use a common interface 409 that includes a knob(e.g., a rotary switch) 418, one or more hard keys 419 for dedicatedfunctions, status LEDs 420 and an audible software alarm speaker 421. IOprocessor 410 may track knob 418 and hard keys 419, and provide the UIsoftware with an interrupt and data during periods of knob and/or hardkey activity. IO processor 410 may also synthesize software alarms andcontrol status LEDs 420 based on commands from the UI software.

An optional internal pulse oximeter module 426, whose external sensor isplaced on the patient's finger, provides monitor data such as pulse rateand oxygen saturation level to user interface processor 403. Userinterface processor communicates with module 426 over a serial interfacesuch as UART 437.

Cradle interface 423 includes a connector 424, for electrically engaginga mating connector on the docking cradle, and a transceiver (e.g., ISOXCVR 425) to allow communication (e.g., via a serial UART interface 438)between the ventilator and the docking cradle electronics at moderatedata rates. DC power may also be transferred through this interface (seecradle power line 441 from connector 424 to power module 483) from thedocking cradle to the ventilator. The ventilator may also provide aremote alarm/nurse call signal through cradle interface 423 to theoutside world.

A non-volatile memory circuit (e.g., NAND FLASH 427) may be included inUI subsystem 400 for long term logging of ventilator events and controlsettings changes (like a “black box” recorder). User interface processor403 may write directly into non-volatile memory 427 via a parallel bus(436), for example.

IO processor 410 may also act as the supervisor for power subsystem 402.For example, IO processor 410 may monitor all power inputs and powersupply outputs, manage the selection of the active input power source(via power source switch matrix 489), and control the two internalbattery chargers (485 and 487). Additionally, IO processor 410 maymonitor the state of the “ON/OFF” and “ALARM SILENCE/RESET” hard keysand drive the “ON/OFF”, “VENT INOP”, “ALARM SILENCE”, “EXTERNAL POWER”,“BATTERY STATUS”, and “CHARGE STATUS” LEDs on common interface 409.

IO processor 410 may act as the device watchdog. For example, in oneembodiment, each subassembly must periodically report good health backto 10 processor 410. In turn, IO processor 410 must periodically reportgood health to alarm driver 412 of alarm system 407. If alarm driver 412fails to receive good health updates, then the audible hardware alarm(INOP) 413 and remote alarm/nurse call outputs (411) are activated.Alarm driver 412 may also trigger a device reset to attempt to restartthe life support function.

3. Power Subsystem

Power module 483 provides power to the ventilator and is connectedthereto by bus 440. The ventilator may be powered from either anexternal DC source (e.g., external power source 492 or cradle interface423) via connector 490, or an internal source (e.g., removable battery491 or bridge battery 486). Bridge battery 486 may be sized to provideseamless operation of the ventilator while removable battery 491 isswapped from connector 488. Two independent internal chargers (485 and487) may be included for purposes of maintaining charge on removablebattery 491 and bridge battery 486. Power supply 484 may include severalswitching and/or linear power supplies to provide the DC voltages usedthroughout the ventilator system.

E. Docking Cradle Electronic Architecture

FIG. 5 is a block diagram of the electrical architecture for oneembodiment of the docking cradle 200. As shown, the docking cradle isdivided into a basic module 500 and a full-featured module 501. Basicmodule 500 provides basic power and status indicators, as well as analarm cable output. Full-featured module 501 provides additionalprocessing power, as well as further connection interfaces, monitoringcapability and support for an additional display monitor. The divisionof features is shown to highlight the range of capabilities that may,but need not be, implemented within the docking cradle. The illustratedfeatures are not intended to be exhaustive, nor do they representrequired features. Different embodiments of the docking cradle mayinclude different combinations and different numbers of features withoutdeparting from the scope of the invention.

In the illustrated embodiment, basic module 500 includes cradleinterface connector 503, which mates electrically with cradle interfaceconnector 424 of the ventilator. DC power is supplied to the ventilatorthrough power line 527 via AC/DC adapter 507, which may receive AC powerfrom an external source (e.g., from a cable attached to a wall outlet).AC/DC adapter 507 may also provide DC power to full-featured module 501via power monitor and controller block 506. The remote alarm/nurse calloutputs from the ventilator (see block 411, FIG. 4) are made availablefor attachment of an external alarm cable (e.g., to plug into a walljack or device in a hospital room) through remote alarm/nurse callinterface 508. If full-featured module 501 is present, then atransceiver (XCVR) circuit 504 may be implemented to facilitatecommunication with the ventilator over the cradle interface connector503. Transceiver circuit 504 may communicate with cradle processor 509over a serial interface, such as a UART interface 526. Hardware drivenstatus LEDs 505 in basic module 500 provide basic device status, such asthe active presence and/or health of AC/DC adapter 507 and of theconnection with the ventilator.

Full-featured module 501 may be implemented to further expand theinterface capabilities of the docking cradle to include, for example,the following options: support for an additional display monitor (502),memory expansion by the addition of one or more memory cards 575 (e.g.,compact FLASH memory cards) in memory card slot(s) 514, an additionalpatient monitoring interface 516, an internal ETCO2 monitor 518 (coupledto an external ETCO2 sensor 579), and a modem 520 (e.g., for remoteaccess via telephone).

A software program executed by cradle processor 509 controls theoptional features of full-featured module 501. Cradle processor 509 mayinclude (either on-chip or off-chip) data SRAM memory, program FLASHmemory, and battery-backed SRAM. The FLASH memory may be in-systemprogrammable, via the ISP/debug interface (service port) 517, tofacilitate manufacturing, service and field software updates.

In full-featured module 501, power supply 521 may be provided to performDC-DC conversion to generate all of the supply voltages needed by thefull-featured module circuitry. Software driven status LEDs 522 may beincluded to show the on/off state and health of the module electronics.

To provide support for an additional display monitor 502, full-featuredmodule 501 may be equipped with monitor controller 510. Monitorcontroller 510 includes an LCD controller 511 (assuming the monitor isan LCD monitor), backlight DAC 512 and touch screen ADC 513. LCDcontroller 511 supplies data and control signals to LCD panel 523 overLCD bus 528 and control (CTL) bus 529, respectively; backlight DACdrives backlight inverter circuit 524; and touch screen ADC 513 controlstouch screen panel 525, as well as receiving touch screen data, over TSbus 530. In other embodiments, additional or different features may beembodied within full-featured module 501.

F. General Software Architecture for Ventilator System

In one or more embodiments, the ventilator and docking cradle containembedded software (and/or firmware) that control the respective hardwareand determine the operating characteristics of the system. This softwaremay be split between multiple processors distributed throughout thesystem on various subassemblies. FIG. 6 is a block diagram illustratingthe context of the general software architecture of a ventilator system,in accordance with one or more embodiments of the invention.

In FIGS. 6A and 6B, the software for the ventilator system isdistributed among the following processors: user interface processor403, IO processor 410, ventilation processor 443, blender processor 462,exhalation processor 455, pressure processor 471, blower processor 445,and cradle processor 509. Various functions of the software executed bythose respective processors are described below. The functions describedare presented for illustrative purposes only and should not beconsidered as either the only nor as required functions for allembodiments. For ease of discussion, the software running on eachprocessor will be referred to with reference to the name of theprocessor (i.e., the software executing on the user interface processoris referred to as the user interface software, the software running onthe blender processor is referred to as the blender software, etc.).

The user interface software (executing on user interface processor 403)may be configured to communicate with 10 processor 410 (via bus 439, asshown in FIG. 4) and cradle processor 509, as well as to sendventilation control data (e.g., settings and alarm limits) toventilation processor 443. The user interface software may storeapplication code received from cradle processor 509 into FLASH memory427, and update application code for IO processor 410, ventilationprocessor 443, blender processor 462, exhalation processor 455, pressureprocessor 471 and blower processor 445. The user interface software mayalso store trend data, vent settings and user configuration data innon-volatile RAM (NVR) 601, and may log all events, such as controlchanges, alarms and failures, in the “black box” portion of FLASH memory427. The user interface software drives the LCD user interface (LCD 429,touch panel 431 and backlight 433), for example, to display alarm dataand/or monitored data received from ventilation processor 443.

The IO software (executing on IO processor 410) may be configured tocommunicate with user interface processor 403 to provide an intelligentcontroller for attached peripheral circuits and devices. For example,the IO software may provide low level drivers for status LEDs 420,common buttons (or keys) 419, knob 418 and speaker 421. In addition, theIO software may be configured to refresh LED matrix 414, scan key matrix415, and control the power switch matrix 489 and battery charger(s) 603(485, 487).

The ventilation software (executing on ventilation processor 443) may beconfigured to control primary functions, such as the generation ofbreaths, implemention of the pressure servo, and sequencing of maneuvers(e.g., nebulizer activation, I-hold (inhalation hold), E-hold(exhalation hold), etc.). The ventilation software may also beconfigured to compute monitored parameters, compare monitored values toalarm limits, and schedule auto zero functions for pressure processor471.

The blender software (executing on blender processor 462) may beconfigured to control nebulizer valve 467 and implement the blendingservo to control blend valves 468. The blender software may also monitorand calibrate the O₂ transducer 465, manage calibration of the FIO₂sensor 469 and forward FIO₂ data to ventilation processor 443.

The exhalation software (executing on exhalation processor 455) may beconfigured to implement the PEEP servo for control of PEEP in-valve 604and PEEP out-valve 605 based on the input from pilot pressure transducer458. The exhalation software-may also control exhalation valve 459 andmanage calibration of the pilot pressure transducer and the PEEP servo.

The pressure software (executing on pressure processor 471) may beconfigured to provide calibrated trigger pressure readings and flowsensor pressure readings from flow transducer 477, calibrated blowerdifferential pressure readings from blower transducer 607 and calibratedairway pressure readings from airway transducer 606 to ventilationprocessor 443. The pressure software may also implement auto zero andpurge functions with auto zero valves 473 and purge valves 474.

The blower software (executing on blower processor 445) may beconfigured to implement the speed servo and commutate the blower motor453. To facilitate implementation of the speed servo and commutation ofmotor 453, the blower software may also calibrate the motor positionsensors (e.g., Hall sensors 452) and compute rotor position and speedfrom the outputs of the motor position sensors 452. The blower softwaremay also implement active braking of motor 453 and active soundcanceling (e.g., using inputs from microphones 451 and generatinganti-noise outputs via speakers 450.

The cradle software (executing on cradle processor 509) may beconfigured to communicate with user interface processor 403, and todisplay ventilation data (e.g., waves, loops, data, summary and trends)on LCD display 523. The cradle software may also be configured to storetrend data and print images on memory card 575. The cradle software maycollect ETCO2 data from ETCO2 monitor 518 and transmit that data to theventilator via user interface processor 403. Additionally, patient dataand alarms may be forwarded to other patient monitor systems (e.g., viaport 516).

II. Ventilator Pneumatics in One Embodiment

The ventilator pneumatics comprise several electromechanicalsubassemblies in one or more embodiments of the invention. Ventilatingfunctionality is provided by computer control of the pneumatic functionsof those electromechanical subassemblies. FIG. 7 is a pneumatic diagramof one embodiment if the ventilator.

In the system of FIG. 7, room air is drawn in through inlet filter 700,after which the air travels through a combination accumulator/silencerchamber 701 where the air may be mixed with oxygen. Chamber 701 alsoserves to absorb noise produced on the inlet side of Roots blower 702.Roots blower 702, driven for example by a brushless DC motor, is arotary positive displacement machine that adds energy to the gas mixtureand supplies gas to the patient at the desired flow and pressure.

In one embodiment, Roots blower 702 may be characterized according tospeed, flow, differential pressure and the associated flow data storedin electronic memory for use by ventilator processor 443 in alternatelyaccelerating and decelerating the blower to effect inspiration andpermit exhalation. Analog position sensors (e.g., Hall sensors) measurethe rotor position within the motor, from which blower processor 445 maycompute the rotational speed of Roots blower 702. Differential pressuretransducer 703 measures pressure across the blower. The ventilatorprocessor 443, working in conjunction with blower processor 445, mayadjust the blower speed throughout the inspiratory phase to obtain thedesired flow, volume and pressure. Solenoid valves 704 and 705 provideauto-zero capability for the differential pressure transducer 703.

Silencer chamber 706 on the gas outlet side of Roots blower 702 reducesblower noise. The gas then travels through bias valve 707, set, forexample, on or about 5 cmH2O.

Patient flow transducer 708, a fixed orifice differential pressure typetransducer, measures the flow to and from the patient. Overpressurerelief valve 709 and sub-ambient relief valve 710 are internal andprovide mechanical fail-safes to insure patient safety in the event ofmajor ventilator malfunction. MIP/NIF lockout coil 711 is included insub-ambient relief valve 710 to prevent opening of the valve duringmaximum inspiratory pressure (MIP) procedures.

Pressure transducer module 712 provides the basic pressure measuringcapabilities of the system. For example, three Piezo-resistive pressuretransducers form flow sensor differential pressure transducer 713 tomeasure differential pressure across patient flow transducer 708 and anairway gauge pressure transducer 714 to gauge the pressure at thepatient airway. Solenoid valves 715 and 716 provide auto-zero capabilityfor flow sensor differential pressure transducer 713, while valves 717and 718 periodically send dry gas from the blower outlet through thepatient flow transducer sense lines as part of a purge cycle.

Exhalation control module 719 allows the patient to exhale in accordancewith the desired PEEP. During inspiration, exhalation control solenoid720 feeds gas pressure from the blower outlet to the balloon diaphragmof exhalation valve 721, which closes the exhalation valve. Duringexhalation, pilot pressure from pilot pressure accumulator 722 is fed tothe balloon, which establishes the PEEP level. The pilot pressure inaccumulator 722 is controlled through pulse-width modulation (PWM) ofpilot-in solenoid valve 723 and pilot-out solenoid valve 724, usingfeedback from pilot pressure transducer 725.

Oxygen blending and nebulizer drive are controlled in blender module726. Pressurized gas is received from an external source, filtered, andfed into the chambers of noise attenuation system 701 under the PWMcontrol of solenoid valves 727, 728, 729 and 730 having associatedorifices. Each solenoid valve orifice may be characterized duringinitial assembly, and the associated flow data may be stored inelectronic memory on a PCB within module 726. O₂ pressure transducer 731measures the valve inlet pressure. Using inlet pressure, the storedorifice characterizations, and PWM, the blender controller can deliverthe range of oxygen flow desired. Nebulizer drive solenoid valve 732 andits associated orifice may deliver content, such as aerosolizedmedication, to the drive port of valves 727-730 during the inspiratoryphase. The quantity of content may be, for example, on or about 6 lpm ofoxygen flow. System software may adjust the delivery of oxygen andvolume to compensate for the added nebulizer flow.

As previously described, variable speed Roots blower 702 is alternatelyaccelerated and decelerated by ventilator processor 443 as necessary toeffect inspiration and expiration. In an alternate embodiment, Rootsblower 702 is maintained by ventilator processor 443 at a relativelyconstant speed, generating a relatively constant flow of gas at a flowrate and pressure suitable for ventilating the lungs of a patient. Adownstream flow control valve is utilized to control the flow of gas tothe patient, opening to effect inspiration and closing to permitexhalation. In this alternate embodiment, the unique pressure and flowoutput of each Roots blower 702 need not be measured during productionand no individualized blower characterization data need be stored foruse by the ventilator processor 443.

III. Exhalation Control Servo Embodiment

One or more embodiments of the invention implement an exhalation controlservo to generate an actual PEEP pressure from a desired PEEP pressurevalue. The desired PEEP pressure value is a digital value representativeof a PEEP pressure. The actual PEEP pressure is a controlled force perunit area generated from the blower pressure of Roots blower 702. Theexhalation servo comprises electromechanical apparatus for achievingthis conversion from the digital domain to the pneumatic domain.

FIG. 8 is a block diagram showing an exhalation servo loop, inaccordance with an embodiment of the invention. The exhalation controlservo of FIG. 8 includes a software control block 800, a mechanicalassembly 801 and an electrical assembly 802. In operation, softwarecontrol block 800 receives the digital desired PEEP value 804 (e.g.,from ventilator processor 443) and a digital value of the current rawpilot pressure 808, and generates a charge command 805 for increasingthe output pressure of the servo loop and a discharge command 806 forreducing the output pressure. Commands 805 and 806 are in electricalform (e.g., digital).

Mechanical assembly 801 receives the charge and discharge commands (805,806) from software control 800, as well as a physical blower pressure803, in pneumatic form. Mechanical assembly 801 applies blower pressure803 in accordance with the charge and discharge commands to generate apilot pressure feedback value 807 and actual PEEP value 809, both inpneumatic form. Electronic assembly 802 transforms pilot pressure 807into raw pilot pressure signal 808, in digital form for processing bysoftware control 800.

FIG. 9A is a block diagram of mechanical assembly 801, in accordancewith an embodiment of the invention. In mechanical assembly 801, chargecommand 805 is applied to charge valve 723 to control the amount ofblower pressure 803 released into pilot chamber 722. Discharge command806 is applied to discharge vale 724 to control the release of pressurefrom pilot chamber 722. In one embodiment, charge command 805 anddischarge command 806 are implemented as PWM signals. Pilot chamber 722accumulates the pressure effects of opening and closing valves 723 and724. The accumulated pressure is output as pilot pressure 807. Chamber900 may embody the balloon diaphragm of the exhalation control valve,which asserts the actual PEEP pressure 809.

FIG. 9B is a block diagram of an embodiment of electronic assembly 802.The pilot pressure 807 is converted into pilot pressure sense signal 901by pressure transducer 714. Pre-amplifier 902 amplifies pilot pressuresense signal 901 and low-pass filter 903 removes any noise and upperharmonics in the amplified signal. The amplified and filtered sensesignal is then sampled by sample-and-hold circuit 904 and subsequentlyconverted into the digital raw pilot pressure value 808 in ADC block905.

FIG. 9C is a block diagram of an embodiment of software control block800. In block 906, the desired PEEP value 804 is applied to a functionto generate desired pilot pressure value 907. The function implementedwithin block 906 may be a simple table look-up based on known (i.e.,calibrated) values of pilot pressure for a given PEEP value.Alternatively, that function may be a mathematical model thatapproximates the inverse of the relationship between a pilot pressureinput into chamber 900 and the PEEP value that results.

Digital low-pass filter 908 receives raw pilot pressure signal 808 andbandlimits that signal to maintain a desired servo loop response. Block909 implements a mathematical function that approximates the inverse ofthe characteristics of the transducer in block 714. Any variance inpilot pressure values due to the behavior of the transducer may becorrected by block 909.

The mathematical model for block 909 may be created by calibrating thetransducer during production and storing raw and actual pilot pressurevalues. A mathematical equation may then be constructed to approximatelyreverse the effects of the transducer by determining coefficients forthe equation through the application of least squares curve fitting orsimilar techniques on the calibration data.

In block 911, the desired pilot pressure 907 and the actual pilotpressure 910 are compared to determine an error value, and that errorvalue is applied to a control algorithm (e.g., a PI or PID algorithm) togenerate charge command 805 and discharge command 806. In oneembodiment, the binary states of the charge and discharge commands aredetermined at periodic intervals. If the measured pilot pressure exceedsthe desired pilot pressure by a threshold amount, then the dischargecommand is asserted during that interval, whereas if the measured pilotpressure falls below the desired pilot pressure by more than a thresholdamount, the charge command is asserted during that interval. When themeasured pilot pressure resides within the threshold range of thedesired pilot pressure, neither command is asserted (maintain status quofor current interval).

IV. Embodiment of Roots Blower Assembly

The present invention involves the precision speed control of anelectric motor that may be used to drive a compressor in a mechanicalventilator. Mechanical ventilators may have various modes of operation,e.g., pressure control and volume control. One common thread amongstmost mechanical ventilators is that the desired operating mode isachieved by controlling the gas flow rate produced by the gascompressor. An example of a suitable compressor control system for ablower assembly is further described in U.S. patent application Ser. No.10/847,693, filed May 18, 2004, the specifications and figures of whichare herein incorporated by reference.

In one embodiment, the compressor motor is a brushless DC (BLDC) motordriving a Roots blower used as a compressor in a portable mechanicalventilator. The flow rate and pressure provided by the compressor arecontrolled by the speed of the BLDC motor. Unlike in prior art systemswhere digital Hall effect sensors are used to provide discrete samplesof the rotor position and separate speed transducers are used to providespeed feedback of the BLDC motor, embodiments of the present inventionmay employ analog sensors (e.g., analog Hall effect sensors, anisotropicmagneto-resistive (AMR) sensors, etc.) to provide continuous rotorposition and speed feedback for closed loop control.

FIG. 10 is a block diagram of a motor/compressor system in accordancewith an embodiment of the present invention. In this illustration, themotor/compressor system comprises Roots blower 1002 coupled to BLDCmotor 1004. Gas (i.e., air) enters Roots blower 1002 via inlet 1008. Theair from inlet 1008 is compressed by Roots blower 1002, and then passedto the patient and/or other sections of the mechanical ventilatorthrough outlet 1010. Fluid communication paths are provided from theinput of Roots blower 1002 to solenoid valve 1012, and from the outputof Roots blower 1002 to solenoid valve 1014. Ambient air pressure isalso channeled to solenoid valves 1012 and 1014 via ambient inlets 1016and 1018, respectively.

The output fluid communication channels of solenoid valves 1012 and 1014are provided to blower differential pressure transducer 1040 to convertthe pressure differential between the two channels into an electricalsignal representative of that pressure differential. During normaloperation, transducer 1040 measures the difference between the outputpressure and input pressure of Roots blower 1002. By controllingsolenoid valves 1012 and 1014, transducer 1040 can also measure thepressure difference between the two ambient pressure inlets during an“auto-zero” phase of transducer 1040. Processor 1020 provides control ofsolenoid valves 1012 and 1014, with solenoid drivers 1032 transformingthe digital control signals from processor 1020 into power DC signalscapable of driving the solenoid valves.

Absolute pressure transducer 1022 and temperature transducer 1024generate electrical signals representing the absolute pressure level andthe temperature. Each of transducers 1022, 1024 and 1040 are coupled totransducer (XDCR) interface block 1026, which may provide signalamplification and filtering of the analog signals that are then providedto A/D (analog-to-digital) converter circuit 1038. A/D converter 1038transforms the analog signals into digital values that may be processedby processor 1020.

In addition to A/D converter circuit 1038, Processor 1020 also has thefollowing associated circuitry: flash memory 1048, JTAG test circuitry1046, random access memory (RAM) 1044, and UARTs (universal asynchronousreceiver-transmitters) 1042 and 1036. External JTAG connector 1050 iscoupled to JTAG circuit 1046 to facilitate hardware tests and debuggingin accordance with the JTAG standard. Telemetry connector 1052 iscoupled to UART 1042 for the transmission of measured ventilatorparameters to a remote system, e.g., for monitoring purposes.Communication and power connector 1054 is coupled to UART 1036 forfacilitating further external communication with the ventilator system,e.g., for operational testing and control. Connector 1054 also providesany necessary power signals to the motor/compressor system (e.g., 3.3,5.0 and/or 15 VDC (volts DC)).

Analog sensors 1006 (e.g., analog Hall effect sensors) are arranged on aPC board in a circular pattern perpendicular to the rotor shaft of BLDCmotor 1004 and adjacent to a two-pole magnet attached to the end of therotor shaft. Analog sensors 1006 provide measurements needed forcomputation of BLDC rotor position. The analog outputs of sensors 1006are passed through sensor interface 1028 (e.g., for amplification andfiltering), and then into A/D converter circuit 1038, where the analogsensor signals are converted into digital values for processing withinprocessor 1020.

Processor 1020 executes software instructions to implement certainelements of the motor/compressor control loop. Processor 1020 may beimplemented, for example, with a general purpose processor or with adigital signal processor (DSP). Other embodiments may implement thefunctionality of processor 1020 in firmware (e.g., instructions storedin an EPROM) or as equivalent logic in a hardware device (e.g., an ASIC(application specific integrated circuit) or an FPGA (field programmablegate array)).

Processor 1020 receives the digitized sensor signals and pressuremeasurements via A/D converter block 1038 (values may use RAM 1044 fortemporary storage), and determines an appropriate speed control valuebased upon the control process implemented (e.g., pressure control orvolume control). Processor 1020 also generates the appropriatecommutation control signals given the current commutation state, andmodulates the pulse widths of those commutation control signals based onthe speed control value. The modulated commutation control signals areprovided to three-phase inverter 1030.

Three-phase inverter 1030 generates drive signals for the individualstator coils in BLDC motor 1004, as previously described. The system mayalso include a current limit circuit 1034 coupled to three-phaseinverter block 1030.

FIG. 11 is an exploded view of the physical structure of a Roots blower,in accordance with an embodiment of the invention. As shown, structure1100 includes the BLDC motor. The stator of the BLDC motor surroundshollow bore 1108, into which a rotor 1101 is inserted duringmanufacturing. Rotor 1101 spins under the influence of the energizedstator coils within the BLDC motor. Stabilizer 1102 supports therotating axis shared by rotor 1101 and Roots blower impeller 1103. Theshared axis forces impeller 1103 to rotate when the BLDC motor forcesrotor 1101 to rotate.

Impeller 1103 rotates within Roots blower housing 1104, with one end ofthe impeller axis coupled to gears 1105. A second impeller (not shown)is also coupled to gears 1105 such that the second impeller rotates inthe opposite direction of impeller 1103. During operation, the rotationof the impellers forces air to flow between the impellers withadditional energy, creating pressure. Openings in either side of housing1104 provide the air input and output paths.

As shown, the elements of the blower assembly are coupled to surroundingstructures in the lateral direction by broad connectors 1106, and in thelongitudinal direction by long connectors 1107. The increased size ofthose connectors provides greater support for the apparatus, whileproviding dampening of vibrations due to the motion of the blowerapparatus.

FIG. 12 illustrates the interlocking nature of the Roots blowerimpellers 1103 and 1203. The shared axis of impeller 1103 and rotor 1101is visible in this image, showing the mechanism by which the Rootsblower impellers are driven. Engagement of gears 1201 and 1202 providesthe transfer of opposing rotational energy from the axis of impeller1103 to the axis of impeller 1203.

V. Noise Reduction

Because Roots blowers are relatively noisy, and because embodiments ofthe invention are designed for use in close proximity to the patient,one or more methods and features for dampening the noise generated bythe blower may be implemented in embodiments of the invention. Suchmethods and features may include forming the blower rotors with ahelical twist (as shown in FIG. 12), and using multiple sound mufflingtechniques, such as the anti-noise cancellation methods describedpreviously.

Additionally, embodiments of the invention may include the use ofperforated tube mufflers, in which numerous perforations protrude fromthe body of each perforated tube at right angles in the form of smalltubes, creating a longer effective muffling pathway capable ofefficiently attenuating sound waves without concomitant increase inmuffler weight and size. The perforated tube mufflers are preferablyconstructed of a lightweight polymer or other sturdy but lightweightmaterial.

FIG. 13A shows a view of the pneumatic pathways and noise reductionchambers of one embodiment of the invention. As shown, air enters theventilator through filtered inlet 1300, and traverses a twistedpneumatic path until it reaches the bottom of silencer chamber 1303.Near the top of silencer chamber 1303, the air is directed into an inletport of the Roots blower assembly 1302. The compressed air is outputfrom the Roots blower assembly into the upper portion of silencerchamber 1304, and then directed on from the bottom (1301) of chamber1304.

Silencer chambers 1303 and 1304 each include two perforated mufflertubes 1305 and 1306 positioned in parallel, e.g., with one above theother. FIG. 13B illustrates the silencer chambers with the top tube(1305) removed, providing a clearer view of underlying tube 1306. Theinput to each silencer chamber is through one end of tube 1305, with theexit being through the opposing end of tube 1306. The air must thereforeflow out of tube 1305 and in through tube 1306. The pressure transientsassociated with compressor noise are dampened by the resistancepresented by the small tubular perforations. Further, the coherence ofthe noise pressure waves is disrupted by the forced traversal ofmultiple small pathways of varying lengths. The varying length pathwayscause the air flow of the respective pathways to recombine out of phasewith each other, diffusing the previously coherent noise. As a result,much of the compressor noise is attenuated during transit of thesilencer chambers.

Embodiments of the invention may also include graduated slots in thehousing of the Roots blower which permit a smooth, gradual backflow ofgas as the leading edge of the blower rotors approach the blower outletport, thus reducing the typical Roots blower pulsing effect responsiblefor much of the noise. The graduated slots in the housing of the Rootsblower maximize noise reduction while minimizing the reduction inefficiency attendant upon permitting gradual backflow into the blowerchambers during rotation.

FIGS. 14A-14D provide different views of the Roots blower housing 1400.Orifice 1401 faces the direction of the BLDC motor, and receives thepair of impellers. In the opposing face 1402 of housing 1400, twoorifices are provided through which the axes of the impellers extend toengage gear structure 1105. perpendicular to the axis defined by orifice1401 and opposing face 1402, an air inlet 1403 and a compressed airoutput port 1404 are provided. The inlet and output ports are configuredwith an initial circular indentation 1405, e.g., to receive a tubularair guide apparatus. Within the circular indentation is an orifice 1406having a roughly triangular cross-section at the level of indentation1405, and a curved wing-shape where the triangular cut-out meets thedual-rounded chamber encompassing the rotating impellers. Also, a groove1407 is formed on the inside of orifice 1406 roughly midway along theside of the triangle, aligned in the same plane as the stacking of theimpellers. Grooves 1407 are deepest at the edge of triangular orifice1406, and gradually diminish to the level of the inner chamber away fromorifice 1406.

The above techniques, methods and features reduce the noise commonlyassociated with Roots blowers, minimizing any auditory discomfort to thepatient, thus permitting the ventilator device to be used in closeproximity to a patient without adding significantly to the weight ordimensions of embodiments of the invention, and thereby facilitatingportability.

The employment in the ventilator of a Roots blower, in combination withthe noise reduction techniques described above, permits improvedminiaturization of the ventilator heretofore unachievable withoutsacrificing sophisticated ventilation modes or patient comfort.

Thus, a portable ventilator has been described. Particular embodimentsdescribed herein are illustrative only and should not limit the presentinvention thereby. The invention is defined by the claims and their fullscope of equivalents.

We claim:
 1. A portable ventilator, comprising: a ventilator housingcomprising a Roots-type blower having helical rotors, and the ventilatorhousing comprising a first display device and a cradle interface; adocking cradle having a ventilator interface configured to engage thecradle interface; and a second display device coupled to the dockingcradle, wherein said Roots-type blower further comprises analog sensorsarranged in a circular pattern, wherein said analog sensors providecontinuous rotor position and speed feedback for closed loop control. 2.The portable ventilator of claim 1, wherein the docking cradle comprisesa power supply for providing electrical power to the portableventilator.
 3. The portable ventilator of claim 2, wherein the portableventilator further comprises: a battery that provides the electricalpower to the portable ventilator when the portable ventilator isdetached from the docking cradle.
 4. The portable ventilator of claim 1,wherein the cradle interface includes a removable memory card slot for aremovable memory card configured to allow transfer of patientinformation between the portable ventilator and a personal computer. 5.The portable ventilator of claim 1, wherein the cradle interfaceincludes a patient monitor interface configured to support a remotepatient monitoring system.
 6. The portable ventilator of claim 1,wherein the cradle interface includes a remote alarm interface.
 7. Theportable ventilator of claim 1, wherein the cradle interface includes aservice diagnosis port.
 8. The portable ventilator of claim 1, whereinthe cradle interface includes flash memory capability to facilitate atleast one of manufacturing updates, service updates and field softwareupdates.
 9. The portable ventilator of claim 1, wherein said at leastone analog sensor is an analog Hall effect sensor.
 10. The portableventilator of claim 1, wherein said at least one analog sensor is ananisotropic magneto-resistive (AMR) sensor.
 11. The portable ventilatorof claim 1, wherein said at least one analog sensor is a plurality ofanalog sensors.
 12. The portable ventilator of claim 1, wherein saidventilator housing comprises graduated slots in said housing.
 13. Theportable ventilator of claim 1, further comprising an additional patientmonitoring interface.
 14. The portable ventilator of claim 1, furthercomprising an arm connected to said docking cradle wherein said seconddisplay device is coupled to said docking cradle via said arm.
 15. Theportable ventilator of claim 1, wherein the analog sensors are arrangedin the circular pattern perpendicular to a shaft of a rotor of a motorof the Roots-type blower and adjacent to a two-pole magnet attached toan end of the shaft.
 16. The portable ventilator of claim 15, whereinthe analog sensors measure a position of the rotor within the motor. 17.A portable ventilator, comprising: a ventilator housing comprising aRoots-type blower having helical rotors, the ventilator housingcomprising a cradle interface and a first display device configured todisplay a first user interface, wherein said housing further comprisesgraduated slots in said housing; a docking cradle having a ventilatorinterface configured to engage the cradle interface; an arm connected tosaid docking cradle; and a second display device coupled to the dockingcradle via said arm, the second display device configured to display asecond user interface concurrent to the first user interface beingdisplayed on the first display device, wherein said Roots-type blowerfurther comprises at least one analog sensor, wherein said at least oneanalog sensor provides continuous rotor position and speed feedback forclosed loop control.
 18. The portable ventilator of claim 17, whereinthe first user interface displays ventilation data generated by theportable ventilator and the second user interface displays expandedventilation data generated by the portable ventilator, wherein theventilation data is a subset of the expanded ventilation data.
 19. Theportable ventilator of claim 18, wherein the second display device isconfigured to display the second user interface concurrent to the firstuser interface being displayed on the first display device when thedocking cradle is engaged with the cradle interface.
 20. The portableventilator of claim 17, wherein the first display device comprises afirst display screen that is configured to display first graphics andthe second display device comprises a second display screen that isconfigured to display second graphics, the first display graphics beingdifferent than the second display graphics.